This invention relates to detecting unwanted materials, such as refractory pieces or other debris, among cullet which is to be fed to a glass melting tank.
Cullet comprises pieces of broken glass which, in flat glass production, generally originate from breaking up defective sheets or ribbon. These broken pieces of glass which comprise the cullet are usually collected into piles and then used to feed the glass melting tank to avoid wastage of the glass and assist the melting operation. Other sources of cullet stem from accidental breakages at e.g. building sites when buildings are being glazed; or in glass container production from the collection of broken bottles which are required to be recycled. Whatever the source of the cullet is it will be apparent that any unwanted materials must be removed from the cullet before it is fed back into a glass melting furnace. This is relatively simple if the unwanted materials comprise ferrous or non-ferrous metal since a suitable metal detector can be employed to indicate the presence of metal among the cullet. However, non-metallic unwanted materials among cullet are more difficult to distinguish from the glass cullet.
Heretofore, when required the inspection of cullet for the presence of non-metallic unwanted materials has been generally carried out with the unaided eye and when located such materials are physically removed from the cullet prior to re-cycling of the cullet into the glass melting tank. There exiss a need for apparatus which will detect the presence of unwanted materials such as pieces of refractory or other debris among cullet but there are obvious difficulties in achieving this end, which difficulties are not encountered when inspecting a glass sheet or ribbon. An example of apparatus which can inspect for faults in a glass sheet or ribbon is described in UK patent specification No. 1315654, the disclosure of which is incorporated herein by reference. The patent teaches the use of a laser system which scans laser light across the sheet or ribbon as it is moving. A light detector is positioned underneath the sheet or ribbon in a position remote from the normal light entry and exit paths of the light beam from the laser. When the light beam impinges upon a defect the light beam is scattered away from the normal light entry and exit path and part of this scattered light is detected by the light detector. The light detector thus gives a signal indicative of the presence of the defect.
Although it might be desirable if apparatus such as is described in UK Pat. No. 1315654 could be used for the detection of unwanted materials among cullet, there are obvious difficulties in differentiating between light scattered by the cullet itself and light scattered by unwanted materials such as refractory debris. It is perhaps for this reason that heretofore no automatic method or apparatus using a light beam has to the present inventors' knowledge been satisfactorily employed for the detection of refractory or other debris among cullet. It is an object of the present invention to provide such method and apparatus.